The existence of large numbers of sites, with soil or other media such as ballast pitch/tar residue, extensively contaminated by polychlorinated biphenyls, hereinafter referred to as “PCBs”, requires economical cost effective treatment methods. Although incineration has been shown capable of destroying PCBs, this form of PCB treatment has been implicated in chlorinated dioxin and dibenzofuran emissions and has been banned for use in certain countries such as Australia and Japan (Costner, Pat et al., 1998, “Technical Criteria for the Destruction of Stockpiled Persistent Organic Pollutants”, Third Meeting of the Intersessional Group Intergovernmental Forum on Chemical Safety, Yokohama, Japan, Dec. 1–4, 1998; see also “Survey of Currently Available Non-Incineration PCB Destruction Technologies”, United Nations Environment Programme, August 2000). There is a need for cost effective PCB decontamination methods for a variety of media, including soil and ballast residue, which do not involve PCB incineration.
PCBs, (approximate formula C12H5Cl5) were manufactured under various trade names (e.g. Arochlor 1254, CAS No. 11097-69-1) and extensively used in electrical equipment, particularly as a dielectric in transformers and capacitors.
Prior to recognition of their environmentally hazardous nature, PCBs were also used in unconfined applications such as pesticide extenders and fire retardants (see MSDS for Arochlor 1254). In the course of industrial operations, spillage has resulted in significant contamination of soils adjacent to facilities involved in the manufacture and repair of electrical equipment as well as other operations using PCBs.
Another significant source of PCB contaminated materials is fluorescent light ballasts manufactured before 1980. Ballasts are regulated in the US Code of Federal Regulations (CFR) Part 761. A summary is presented in a Minnesota Pollution Control Agency Publication (www.pca.state.mn.us/waste/pubs/4—48f.pdf). PCB ballasts can be processed for metal recovery leaving a concentrated PCB residue.
Currently, industrial materials such as transformer oils can be treated by commercial operation to chemically destroy PCBs by sodium reduction. This allows the valuable base transformer oil to be re-used. For solid wastes, however, the currently available options for management/disposal are principally permanent storage in a secure landfill (e.g. in the United States) or incineration in a suitably controlled, monitored and permitted waste incinerator. The former operation results in a permanent retained liability by the waste generator. Incineration is costly and entails risk of atmospheric emissions.
Regulations regarding classification and acceptable disposal of PCB solid wastes vary by jurisdiction. Some representative regulations for British Columbia, Canada are:
Disposal MethodAllowable PCB level in mg/Kg wasteIncinerator or secure fill>50Industrial fill>2 and <50General Landfill<2
Getman et al. in U.S. Pat. No. 6,049,021 describe remediation of soil contaminated with PCBs. This patent describes the destruction of PCBs in soil using a variety of methods combining the following basic elements:                PCB extraction of soil by liquid ammonia        dissolution of sodium metal into PCB-contaminated liquid ammonia        destruction of PCB in liquid ammonia by dissolved sodium metal        
Although this technique clearly shows high destruction of PCB in soil it suffers from the following problems:                Need to refrigerate ammonia with soil with stirring before addition of sodium metal (see Example 4)        Need to operate with hazardous pressurized anhydrous ammonia gas in a stirred vessel (see Example 2)        Extremely high ammonia dose on soil e.g. 9 litres ammonia per kilogram of soil (see Example 3)        Generation of ammonia containing residual wastes “filtrates” (see Example 2)        Awkward temperature cycling between 0° C. and 20 to 40° C. (see Example 4) or −78° C. (see Example 3)        Awkward, time consuming, multiple soil extractions with ammonia before addition of sodium metal (see Example 4)        
U.S. Pat. No. 5,228,921 issued to Peterson describes a method for extracting organohalogens from organohalogen contaminated solids such as PCBs from PCB contaminated soils. U.S. Pat. No. 5,376,182 issued to Everett et al. describes PCB extraction from PCB contaminated soil with ultrasound at 10 to 60 kilohertz frequency. Although these extraction methods successfully remove PCBs from soil, they do not destroy the PCBs.
PCT application WO 02/22252 of Collings describes ultrasonic destruction of PCBs in a one-step process. However, PCB destruction efficiency is low (e.g. 75% lines 20 to 25, page 10).
Eco Logic at web page www.eco-logic-intl.com in a brochure dated April 2001 and entitled “The TORBED/GPCR combination for Soil, Sediment and Sludge Treatment” describe a multi-step process for removal and destruction of PCBs in solids such as soils as follows:                1. High temperature (e.g. 600° C.) thermal desorption of PCBs from soils by volatilization        2. High temperature (e.g. 875° C.) gas phase reduction of volatilized PCB exhaust gas from 1. with a reducing gas such as hydrogen        3. Scrubbing of exhaust gas from 2. to recover toxic and/or corrosive gases such as hydrogen chloride produced from reduction of PCBs        4. Compression and/or storage of scrubbed exhaust gas from 3        5. Incineration and/or recycling of scrubbed exhaust gas from 4 to steps 1 and/or 2 respectively        
Although the Eco Logic method clearly destroys PCBs in soils it suffers from the following problems:                1. Generation of toxic and/or corrosive exhaust gas (e.g. hydrogen chloride) and spent scrubber solutions        2. Use of potentially explosive hydrogen gas at high temperature        3. Five or more processing steps        4. Two energy intensive, high temperature processing steps        
U.S. Pat. No. 4,941,134 issued to Nyberg et al. describes a sonic generator for the transmission of energy into fluid mediums using a “resonating bar” or probe (see FIG. 6A). U.S. Pat. No. 5,005,773 issued to Nyberg et al. describes a method for using this sonic generator in combination with grinding media to effect pulverization of solids contained in a grinding chamber mounted “axially” to the resonant member (see FIG. 9a and lines 25 to 26 plus 33 to 34 on page 5).
U.S. Published Patent application No. 2003/0036672 and Canadian Patent application No. 2,316,409 to Sim et al. describes the destruction of PCBs in ballast tar/pitch using alkali dispersions of sodium, lithium or potassium. This technology suffers from the following serious disadvantages:                Use of sodium dispersions that are 2 to 4 times more expensive than sodium metal ingots and hazardous to use due to their speed of reaction with parasitic agents such as water and certain oxygen containing organics (e.g. phenolics or carboxylic acids) in the tar/pitch        Use of cosolvents (e.g. iso-octane, methanol and isopropanol—see claim 8) which boil or evaporate at suggested processing temperatures e.g. 90° C. (page 2 section [0018] of US application) resulting in wasted solvent and or safety issues due to toxic or flammable vapour discharge        No drying of tar/pitch to remove entrained moisture parasitic to use of alkali such as sodium and resulting in serious potential safety hazards such as hydrogen discharge from the reaction of alkali metal with water at levels in air above its explosive limit        Lack of inerting at the start of alkali contact with the PCB contaminated media resulting in a potential safety hazard due to potential hydrogen discharge above its explosive limit        Contradictory teachings with the applications—page 1 section [0012] of the US application states that the teachings of copending Canadian application 2,316,409 “are incorporated herein in their entirety”. Claim 1 of the Canadian application specifies the operation “below flash point of said contents”. The flash point of methanol, iso-octane and isopropanol suggested in claim 8 of the US application, are according to the Merck Index 12° C., −12° C. and 11.7° C. respectively which are 78° C. lower than the recommended processing temperature.        
There is a need for a low temperature process, especially a process suitable for mobile processing of media at the site of contamination, which can quickly extract and efficiently destroy PCBs in a minimum number of processing steps to reduce the size of equipment and its cost.